Image-processing method and apparatus, and image-forming apparatus

ABSTRACT

In an image-processing method and apparatus, dots forming a step-change part of an outline of an image of characters and/or graphics which image is subjected to half-tone processing are detected, and dots surrounding the detected dots forming the step-change part are transformed into respective dot data each having a size that is smaller than a size of the detected dots forming the step-change part. In the image-processing method and apparatus, one of different transformation methods is selected according to an inclination of the outline in order to produce the dot data in the transforming.

TECHNICAL FIELD

The present invention generally relates to an image-processing methodand apparatus and an image-forming apparatus, and more particularly toan image-processing method and apparatus and an image-forming apparatusfor performing image formation through the ink-jet printing method.

BACKGROUND ART

Conventionally, the ink-jet printing has been used because high-speedprinting is possible without requiring special fixing processing for theplain paper, and the noise occurring at the time of printing issufficiently low. The attention to the ink-jet printing is attracted forthe use in office automation devices.

There have been proposed various conventional methods of ink-jetprinting, or some are already commercially produced and used. Accordingto such ink-jet printing method, the ink-jet head is used in which theink liquid chamber and the nozzle having a passage open to the chamberare formed, and the pressure is applied to the ink in the ink liquidchamber according to image information, so that the small ink drop isdischarged from the nozzle to the printing medium, such as paper orfilm, in order to form an image.

Moreover, there are the serial ink-jet printer and the line ink-jetprinter classified according to the head composition. In the serialink-jet printer, the ink-jet head is scanned the width direction ofpaper (main scanning) and the paper is transported after one or morescanning lines are made to form the following printing line.

On the other hand, in the line ink-jet printer, the nozzle is formed tocover mostly the width of paper, and the paper is transported to performthe printing without scanning the ink-jet head in the width direction ofpaper. This printer is advantageous in that one printing line in thewidth direction of paper is formed at once and the printing speed ishigh. However, the size of the whole printer becomes large since thehead itself becomes large. And, in order to perform printing at a highresolution, it is required to make the arrangement of the nozzle itselfI a high-density arrangement, and there is the problem that themanufacture cost of the head becomes high.

In contrast to the line ink-jet printer, the serial in-jet printer formsthe image with the comparatively small head, and it is advantageous inthat the cost of the printer device can be low, and many serial typeink-jet printers are put in practical use currently.

In the case of the serial type ink-jet printer, the printing speedvaries depending on the resolution of the image, the nozzle density, thedrive frequency that forms the dot, the feed velocity, etc.

Among them, the nozzle density has a restriction of the machiningaccuracy of the nozzle, the liquid chamber, the passage, and theactuator. Especially, in order to carry out division formation at thechannel corresponding to the nozzle in the case of the ink jet methodusing the piezoelectric element, there is only the method of usingformation of the thin film (piezoelectric element PZT) by printing orthe mechanical machining of dicing etc.

Compared with the bubble jet (R) method (or thermal ink jet method)formed according to the semiconductor process, the nozzle density of theink jet method becomes low. The maximum of the nozzle density of theink-jet head using the piezoelectric element is currently about 360 dpi.

By the way, in order to increase the printing speed, using the strokewhich forms the printing region by one scanning is desirable. Forexample, when forming an image with the resolution of 300 dpi in thesub-scanning direction using the head with the nozzle density of 300dpi, it is possible to create the image with one scanning of the headbeing made in the main scanning direction (which is called thenon-interlaced method). When forming an image with the resolution of 600dpi using the head with the nozzle density of 300 dpi, it is necessaryto make two main scannings and one sub-scanning (paper feeding), whichis called the interlaced method. The printing speed of thenon-interlaced method is higher than the printing speed of theinterlaced method.

Moreover, there are the one-path printing method in which one printingline in the main scanning direction is formed by making one mainscanning, and the multi-path printing method in which one printing lineis formed by making two or more main scannings. The printing speed ofthe former is higher than that of the latter.

However, in the case of the ink-jet printer using the piezoelectricelement, the nozzle density itself is low as mentioned above. Whencreating the image by using the one-path non-interlaced method in orderto increase the printing speed, the resolution of the image will becomelow inevitably.

When the image density is low, the method of forming one pixel with oneof multiple values is effective for improving the image quality.Examples of the multiple-value method may include the method of changingthe size of one dot itself, the method of discharging the small dottwice or more to form one pixel, the method of changing theconcentration of the ink itself, etc.

However, the multiple-value method is effective for the photographicimage only in improving the image quality, but such effect is hardlyacquired for the images such as graphics or characters.

In the case of characters and graphics, the dot size must be larger thanthe dot size to fill the background part of the image. When a small dotsize is used, it becomes the low-concentration character or graphicimage.

Therefore, in binary images, such as characters or graphics, the problempeculiar to low resolution arises, and in the case of the characterimage especially, the image quality of the character will degrade, andit is difficult to read the character image.

A description will be given of the problem peculiar to low resolution.The printed image of the ink-jet printer is expressed with the dotsformed in the scanning direction of the head, and the conveyancedirection of the recording paper which is the direction which intersectsperpendicularly with it in the shape of a matrix.

When the character is printed as a dot image, the quality of thecharacter varies greatly with the resolution of the image to print. Forexample, the number of the dots which constitute the character when theprinting of the character of the same size is performed at theresolution of 600 dpi is about 4 times larger than that when theprinting is performed at the resolution of 300 dpi. The former printingcan express a fine image, and the character quality is better.

Especially, at the slanting line part of the character, the number ofthe dots arrayed in the shape of stairs is increasing according to theresolution, and the slanting line part of the character in the case ofprinting at 300 dpi is more easily recognized as jaggies or notches.

There is proposed the image output method which improves the quality ofthe output image as disclosed in Japanese Patent No. 2886192. Thismethod is aimed to reducing the jaggies appearing at the outline part ofthe image at the time of low resolution.

In the method disclosed in Japanese Patent No. 2886192, the bit patternof a sample window in the bitmap image of the character is compared witha predetermined bit pattern, and when a match occurs, the central pixelin the sample window is corrected to be the small dot.

Moreover, there is proposed the image forming apparatus as disclosed inJapanese Patent No. 3029522. In the method disclosed in Japanese PatentNo. 3029522, the outline part of the image is discriminated from theblack dot data, and the printing dots other than the edge dots or theblack dots are changed to the small-sized dots.

However, the above-mentioned methods of Japanese Patent No. 2886192 andJapanese Patent No. 3029522 are effective only for the LED printer orthe laser printer as disclosed. This is because in the LED printer andthe laser printer, the toner with a grain size of 10 micrometers or lessis used and there is no spreading of the toner on the plain paper andthe small dot as specified is almost obtained.

Furthermore, it is because it is possible to form the dot of thespecified size in the optimal position by changing the luminescenceposition and length of the laser delicately in the laser printer.

However, in the ink-jet printing device, the spreading of the ink islarger than the spreading of the toner in the laser printer. Moreover,in order to form the dot, the ink-jet printing device requires a longertime than the LED printer and the laser printer, and it is difficult tochange the dot size into a variety of sizes in accordance with a changein the number and length of the driving pulses within the drivingperiod. It is only possible for the ink-jet printing device to changethe dot size into a few kinds of dot sizes at most.

Moreover, for the same reason, the ink-jet printing device is able toform the dot only in the mostly regular position. But changing theposition within one pixel, which can be made freely in the LED printerand the laser printer, is difficult for the ink-jet printing device torealize.

Moreover, there is the smoothing method which is called theanti-aliasing. However, in the case of the anti-aliasing, the dot ischanged with a large number of gradations to create the outline of thecharacter. It is possible to attain highly precise smoothing of theoutline. However, the processing is very complicated and the processingtime is needed for this method. When the high throughput is requiredlike the latest ink-jet printer, this method is unsuitable.

Furthermore, when the dot size is changed and printed by the ink-jetprinting method, the problem arises also in that the dot position on thepaper changes with the dot size. A description will be given of thisproblem.

The pressure acts on the ink in the liquid chamber according to theaction power of a pressure generating unit to give the pressure to theink, and the ink carries out the discharge of the ink-jet printingdevice from the nozzle with the pressure.

The pressure generating unit in the case of the bubble jet (R) method(also called the thermal ink-jet method) is the thermally heatingresistor for generating air bubbles, while the same in the case of thepiezoelectric method is the piezoelectric element which is theelectro-mechanical transducer for deforming the liquid-chamber wall.

In order to change the diameter of the dot with the ink-jet printingdevice, the method of changing the energy supplied to the pressuregenerating unit is usually used. Specifically, the magnitude of thedrive voltage of the pressure generating unit is changed, or the pulsewidth of the driving pulse or the pulse number is changed.

For the method of changing the drive voltage among these methods, aplurality of signal receiving channels to which the changed drivevoltage is supplied are required, and a switching unit for switching andchoosing one of the drive voltages for each of these channels is alsorequired. Hence, the driving element (driver IC) when the method ofchanging the drive voltage is used becomes large.

On the other hand, when the method of controlling the pulse width or thepulse number is used, it is possible to change the pulse width or thepulse number by controlling the switching unit according to the time.This is advantageous in that what is necessary is just to use only oneswitching unit for every channel. Especially, in the case of the ink-jetprinting device using the piezoelectric element, the pulse-widthmodulation or pulse-number modulation method is used.

However, when forming the ink drop which capacity is different (or thediameter of the dot is different) by using the pulse-width modulation orpulse-number modulation method, the length of the driving pulse differs.Although the time that the driving pulse is inputted and the rising ofthe meniscus starts is the same, the time for the discharged ink drop toreach the paper is different since the period from the OFF state of thedriving pulse to the creation of the ink drop is different. As a result,the dot position on the paper varies depending on the dot size.

For this reason, even if the outline part of the character is correctedby using the small printing dot in order to improve the image quality,the small-sized dot is not formed in the requested position, andtherefore the image quality will deteriorate.

DISCLOSURE OF THE INVENTION

An object of the present invention is to provide an improvedimage-processing method and apparatus in which the above-mentionedproblems are eliminated.

Another object of the present invention is to provide animage-processing method and apparatus which realizes high-speed printingof an image forming apparatus using the ink-jet printing method witheffective improvement of the image quality by reducing the step-changepart of the outline of the image of characters and/or graphics which issubjected to half-tone processing.

Another object of the present invention is to provide an image-formingapparatus which realizes high-speed printing using the ink-jet printingmethod with effective improvement of the image quality by reducing thestep-change part of the outline of the image of characters and/orgraphics which is subjected to half-tone processing.

In order to achieve the above-mentioned objects, the image-processingmethod of the invention comprises the steps of: detecting dots forming astep-change part of an outline of an image of characters and/or graphicswhich image is subjected to half-tone processing; and transforming dotssurrounding the dots forming the step-change part detected by thedetecting step, into respective dot data each having a size that issmaller than a size of the detected dots forming the step-change part,wherein one of different transformation methods is selected according toan inclination of the outline in order to produce the dot data in thetransforming step.

The above-mentioned image-processing method may be configured so that inthe transforming step the dot data having the smaller size is added to ablank part of the dots forming the step-change part. The above-mentionedimage-processing method may be configured so that in the transformingstep the dot data having the smaller size is added to a font data partof the dots forming the step-change part.

The above-mentioned image-processing method may be configured so thatthe different transformation methods in the transforming step aredifferent in the size of the dot data produced in the transforming step.The above-mentioned image-processing method may be configured so thatthe different transformation methods in the transforming step aredifferent in the number of dots formed with the respective dot dataproduced in the transforming step. The above-mentioned image-processingmethod may be configured so that the different transformation methods inthe transforming step are different in a level of gradation of the imageof characters and/or graphics.

Moreover, in order to achieve the above-mentioned objects, theimage-processing apparatus of the invention comprises: a detection unitdetecting dots forming a step-change part of an outline of an image ofcharacters and/or graphics which image is subjected to half-toneprocessing; and a transformation unit transforming, according to adetection result from the detection unit, transforming dots surroundingthe dots forming the step-change part detected by the detection unit,into respective dot data each having a size that is smaller than a sizeof the detected dots forming the step-change part, wherein thetransformation unit is provided to select one of differenttransformation methods according to an inclination of the outline inorder to produce the dot data by the transformation unit.

The above-mentioned image processing apparatus may be configured so thatthe detection unit is provided to detect the dots forming thestep-change part of the outline before the image of characters and/orgraphics is subjected to the half-tone processing.

Moreover, in order to achieve the above-mentioned objects, theimage-forming apparatus of the invention includes an image-formationunit forming an image on a recording paper through an ink-jet printingmethod, and a recording-paper conveyance unit conveying the recordingpaper, the image formation unit comprising: a detection unit detectingdots forming a step-change part of an outline of an image of charactersand/or graphics which image is subjected to half-tone processing; and atransformation unit transforming, according to a detection result fromthe detection unit, transforming dots surrounding the dots forming thestep-change part detected by the detection unit, into respective dotdata each having a size that is smaller than a size of the detected dotsforming the step-change part, wherein the transformation unit isprovided to select one of different transformation methods according toan inclination of the outline in order to produce the dot data by thetransformation unit.

The above-mentioned image forming apparatus may be configured so thatthe image formation unit forms the image on the recording paper using anink which is composed of at least pure water, a pigment, a water-solubleorganic solvent, and a polyol or glycol ether with carbon number ofeight or more.

The above-mentioned image forming apparatus may be configured so thatthe image formation unit forms the image on the recording paper using anink which is composed of at least pure water, a pigment, a wettingagent, an anionic or nonionic surface active agent, a water-solubleorganic solvent, and a polyol or glycol ether with carbon number ofeight or more, wherein the ink has a pigment concentration of 6% wt ormore and an ink viscosity of 8 cp or more at 25 degrees C.

According to the present invention, it is possible to reduce thestep-change part of the outline of the image of characters and/orgraphics which is subjected to half-tone processing, so that the imagequality can be improved and high-speed printing of the image formingapparatus using the ink-jet printing method can be realized.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view showing the outline composition of themechanism part of a serial type ink-jet printing device in the preferredembodiment of the invention.

FIG. 2 is a cross-sectional view showing the principal part of theink-jet head in the ink-jet printing device of FIG. 1.

FIG. 3 is a diagram for explaining the nozzle pitch of the ink-jet head.

FIG. 4 is a block diagram showing the composition of the control unit inthe ink-jet printing device of FIG. 1.

FIG. 5 is a block diagram showing the functional composition of each ofthe host computer and the ink-jet printing device.

FIG. 6 is a diagram showing an example of the output character which issubjected to a conventional half-tone processing using 50% for each ofthe large and middle drops.

FIG. 7 is a diagram showing the dot configuration of a slanting part ofthe character which is subjected to the conventional half-toneprocessing using 50% for each of the large and middle drops.

FIG. 8 is a diagram showing the dot configuration of the slanting linepart which is subjected to a half-tone processing in the preferredembodiment of the invention using 50% for each of the large and middledrops.

FIG. 9 is a diagram for explaining the drive waveform of the head.

FIG. 10 is a block diagram showing the composition of the drive circuitof the head which circuit corresponds to the head driving unit of FIG.4.

FIG. 11 is a diagram showing the 5×5 dot window which is used forpattern matching.

FIG. 12 is a flowchart for explaining the processing of the patternmatching.

FIG. 13 is a diagram showing the composition of the driver IC.

FIG. 14 is a diagram for explaining the details of the processing of thepattern matching.

FIG. 15 is a diagram for explaining the case in which the number of thedots which form a straight line between two step-change parts (F, G) inthe slanting line which is subjected to the half-tone processing using50% for each of the large and middle drops is 2.

FIG. 16 is a diagram for explaining the case in which the number of thedots which form a straight line between two step-change parts in theslanting line which is subjected to the half-tone processing using 50%for each of the large and middle drops is 1.

FIG. 17 is a diagram showing an example of the reference pattern in the5×5 dot window.

FIG. 18 is a diagram for explaining the case in which the number of thedots which form a straight line between two step-change parts in theslanting line which is subjected to the half-tone processing using 100%of the small drops is 4.

FIG. 19 is a diagram for explaining the case in which the number of thedots which form a straight line between two step-change parts in theslanting line which is subjected to the half-tone processing using 50%of the middle and small drops is 4.

FIG. 20 is a diagram showing another example of the window used for thepattern matching.

FIG. 21 is a flowchart for explaining the processing of adding the smalldrop to the dot which forms the blank only.

FIG. 22 is a flowchart for explaining the processing of adding the smalldrop to the dot which forms the font only.

FIG. 23 is a flowchart for explaining the processing in which thepattern matching is performed for each bit per window to the bitmap dataas the font data.

FIG. 24 is a diagram showing the example of the slanting line in whichjaggies have been corrected by the processing of FIG. 23.

FIG. 25 is a diagram for explaining the problem that the small drops forthe correction are separated in the slanting line with largeinclination.

FIG. 26 is a diagram showing an example of the correction which iscompatible with reduction of the influence of dot position deviationsand the jaggies correction effect by changing the jaggies correctionmethod by the inclination.

FIG. 27 is a diagram showing an example of the reference patterns withthe 4/1 inclination and the 1/4 inclination.

FIG. 28 is a block diagram showing the composition of the ink-jetprinting device in which the detection unit is provided.

BEST MODE FOR CARRYING OUT THE INVENTION

A description will now be given of the preferred embodiments of theinvention with reference to the accompanying drawings.

With reference to FIG. 1 through FIG. 5, the ink-jet printing device(image forming apparatus) in the first preferred embodiment of thepresent invention will be explained.

FIG. 1 shows the outline composition of the mechanism part of the serialtype ink-jet printing device in the preferred embodiment of theinvention. FIG. 2 is a cross-sectional view showing the principal partof the ink-jet head in the ink-jet printing device of FIG. 1. FIG. 3 isa diagram for explaining the nozzle pitch of the ink-jet head. FIG. 4shows the composition of the control unit in the ink-jet printing deviceof FIG. 1. FIG. 5 shows the functional composition of each of the hostcomputer and the ink-jet printing device.

The ink-jet printing device of this embodiment comprises the frame 1,the guide rails 2 and 3, the carriage 4, and the printing head 5. Theguide rails 2 and 3 are constructed horizontally across the frame 1. Thecarriage 4 is movably connected to the guide rails 2 and 3 so that themovement of the carriage 4 in the direction indicated by the arrow A inFIG. 1 is possible. The printing head 5 is carried on the carriage 4.The movement of the carriage 4 in the direction of the arrow A is drivenby the power source (which is not shown), such as the motor.

The paper (recording paper) 7 which is the printing medium is placedonto the guide board 6, and the paper 7 is received by the platen 10.The platen 10 is equipped with the feeding knob 10 a which is rotatedthrough the drive gear 8 and the sprocket gear 9 by the power sourcewhich is not illustrated. Conveyance of the paper 7 in the directionindicated by the arrow B in FIG. 1 is allowed by the pressure roller 11while the paper 7 is compressed between the pressure roller 11 and theperipheral surface of the platen 10 under pressure.

In the ink-jet printing device of this embodiment, the movement orscanning of the printing head 5 (carriage 4) is carried out in the mainscanning direction (the direction of the arrow A) while the conveyanceof the paper 7 is carried out in the sub-scanning direction (thedirection of the arrow B) so that the ink drop is discharged from theprinting head 5 and an image is printed on the paper 7.

A description will be given of the carriage 4, the printing head 5, theink supply system, etc. in the following.

The carriage 4 is equipped with the printing head 5. The printing head 5comprises the ink-jet heads which carry out the discharging of the inkdrop of each of the colors of yellow (Y), cyan (C), magenta (M) andblack (Bk) respectively, and two or more ink discharge outputs arearranged in the ink-jet heads in the direction which is perpendicular tothe main scanning direction, and the head 5 is mounted with thedirection of the discharge of the ink drop being the downward direction.In addition, the respective ink cartridges for supplying the ink of eachcolor to the printing head 5 are mounted on the carriage 4 in such amanner that they are exchangeable.

The ink cartridge 15 (see FIG. 2) is provided at the top with the airoutlet open to the atmosphere, and provided at the bottom with the inksupply outlet for supplying the ink to the ink-jet head inside. The inkcartridge 15 contains the porosity object inside, and this porosityobject being filled with the ink. The ink of the ink cartridge 15 beingsupplied to the ink-jet head is maintained at a slightly negativepressure by the capillary tube power of the porosity object.

Moreover, the printing head in the present embodiment is constructedusing the separate ink-jet heads of the individual color component inks.Alternatively, the printing head may be constructed as one headcomposition which has the nozzle sequence which carries out thedischarge of the ink drop of each color.

Furthermore, as a printing head (ink-jet head) 5 in which pressurize theink and the ink drop is made to form. Although the electrostatic typewhich is made to carry out displacement of the diaphragm and carries outink pressurization by the static electricity power between the diaphragmwhich forms the liquid-chamber surface of a wall by electric machinetransducers, such as the piezoelectric element, and forms thepiezoelectricity type or the ink passage surface of a wall which carriesout ink pressurization through the diaphragm, and the electrode whichcounters this can be used.

In the present embodiment, a description will be given the case in whichthe piezoelectric type ink-jet head is used.

As shown in FIG. 2 and FIG. 3, the printing head 5 is provided so thatthe nozzle plate 17 in which the plurality of nozzles 16 are formed isattached to the front surface of the liquid-chamber forming member 15which forms the liquid chamber 14.

By giving the pressure to the ink in the liquid chamber 14 by theactuator which is the energy occurrence unit by the piezoelectric devicewhich is not illustrated, the ink in the liquid chamber 14 serves as theink drop 18 from the nozzle 16 of the nozzle plate 17, flies, andadheres to the paper 7 as a dot.

At this time, the desired image is printable by driving selectively theactuator which gives the pressure to each liquid chamber 14.

In this printing head 5, two or more nozzles 16 constitute two or moredot formation units, and the sequence (nozzle sequence) of the nozzle 16is made to intersect perpendicularly to the main scanning direction, andthe pitch between the nozzles 16-16 is represented by 2×Pn.

Moreover, the nozzle sequence distance L Separates on the one head, andis formed in it the two sequences. It is shifting, being configuredalternately and using the nozzle sequence of the two sequences Pn, andthe nozzle sequence of the two sequences can form the image of Pitch Pnin the sub-scanning direction by one scanning and the feed.

Moreover, in order to carry out the movement or scanning of the carriage4 in the main scanning direction, the drive pulley driven and rotated bythe scanning motor and the follower pulley are connected together by thetiming belt, and by fixing this timing belt to the carriage, the two-waymovement of the carriage is carried out according to the forward orreverse rotation of the scanning motor.

On the other hand, in order to convey the paper set on the guide boardto the printing part of the printing head, there are provided the feedroller and friction pad which delivers the paper from the guide board,the guide member which guides the conveyance of the paper, theconveyance roller which conveys the paper from the feed roller, and thetip roller which specifies the delivery angle of the paper from theconveyance roller forced on the peripheral surface of this conveyanceroller and the conveyance roller.

The conveyance roller is driven and rotated by the feed roller throughthe gear train. And the platen roller is configured in order to guidethe paper sent out from the conveyance roller corresponding to thesuccessive range of the main scanning direction of the carriage to theprinting part of the printing head (guide).

Furthermore, at the downstream part of the printing receptacle in thepaper conveyance direction, the conveyance roller which is rotated anddriven in order to send out the paper in the ejection direction, and thespur are arranged. Further arranged are the ejection roller for sendingout the paper to the ejection tray, the spur, the guide member forsecuring the ejection course of the paper, etc.

The printing head is made to drive according to the image signal at thetime of printing, moving the carriage 4. The ink is breathed out in thestopped paper, the one line is printed, and the following line isprinted for the paper after predetermined quantity conveyance.

At the time of the printing end, by receiving the printing end signal orthe signal with which the back end of the paper arrived at the printingregion, printing operation is terminated and the paper is delivered tothe paper.

Moreover, in the position which separated from the printing region bythe side of the transfer direction right end of the carriage, therecovery processing device which is not illustrated for recovering thepoor discharge of the printing head is configured.

To the recovery processing device, it has the cap unit, the suctionunit, and the cleaning unit. During printing standby, it transfers atthis recovery processing device side, and capping of the head is carriedout with the capping unit, and the carriage can prevent the poor inkdischarge by ink dryness by maintaining discharge outlet at the humidstate.

Moreover, by carrying out the discharge of the ink which is not relatedto printing in the middle of printing etc., the ink viscosity in alldischarge outputs becomes fixed, and the stable discharge performance ismaintained.

When the poor discharge occurs, the discharge outlet of the head issealed with the capping unit, air bubbles etc. are sucked out of thedischarge outlet with the ink with the suction unit through the innertube, the ink, garbage, etc. adhering to the discharge outlet face areremoved by the cleaning unit, and the poor discharge is recovered.

Moreover, the attracted ink is sent to the consumed ink tank (not shown)installed on the main part bottom, and absorbed and retained by the inkabsorber inside the consumed ink tank.

A description will be given of the example of the printing device of thepresent embodiment which is not provided with the function of generatingthe dot pattern actually printed in response to the print command of thecharacter or image drawing. That is, the print command from theapplication software executed on the host computer is processed by theprint driver incorporated as the software in the host computer, andrasterized to the data of the printing dot pattern, and such data istransmitted to the printing device so that the printing is performed.

Specifically, the print command of the character or image drawing fromthe application or the operating system in the host computer (forexample, the command in which the position, the thickness, the form,etc. of the line to be recorded are described, or the command in whichthe font, the size, the position of the character to be recorded, etc.)of the character is stored temporarily in the drawing data memory. Inaddition, these commands are described in the specific print language.

The command stored in the drawing data memory is interpreted by therasterizer. If it is the command to print a line, it is transformed intothe printing dot pattern according to the position, the thickness, etc.of the line which are specified by the command. If it is the command toprint a character, the outline information of the correspondingcharacter is called from the font outline data stored in the hostcomputer, and the outline information is transformed into the printingdot pattern according to the size and the position of the characterwhich are specified by the command. Such rasterized dot patterns arestored in the raster data memory.

At this time, the host computer functions to rasterize the command orthe outline information into the data of the printing dot pattern byusing the known rectangular lattice as the basic printing position. Theprinting dot pattern stored in the raster data memory is transmitted tothe ink-jet printing device via the interface.

As shown in FIG. 4, the control unit of the ink-jet printing devicecomprises the printing control unit 23, the head driving unit 24 whichdrives each actuator of the printing head 5, the carriage drive controlunit 25 which carries out driving control of the carriage 4, the linefeed drive control unit 16 which carries out the rotation driving of theplaten 10, and the data-processing unit 27.

The printing data sent from the host computer is stored in the rasterdata memory (which is not illustrated). After the predetermined data isreceived, the stored printing data is supplied via the data-processingunit 27 to the head driving unit 24 so that the ink drop is dischargedfrom the predetermined nozzle outlet 16 of the printing head 5 based onthe printing dot data, the image according to the printing data isprinted on the paper 7. At the same time, the rotation of the platen 10or the conveyance of the paper 7 (the sub-scanning) is controlledthrough the line feed drive control unit 16 and the movement of thecarriage 4 (the main scanning) is controlled through the carriage drivecontrol unit 25.

When the printing on the plain paper is performed by the conventionalink-jet printing device, several image quality problems peculiar to theink-jet printing arise, such as the color-reproduction characteristic,the durability, the light resistance, the ink dryness characteristic,the character blot (feathering), the color boundary blot (colorbleeding), the double-sided printing characteristic, etc. of the image.Furthermore, when the high-speed printing on the plain paper is carriedout, it is very difficult to satisfy all these characteristics.

Moreover, the ink commonly used for the ink-jet printing contains thewater as the major component, the colorant, and the wetting agents, suchas glycerol, for the purpose of prevention of clogging.

As the colorant, there are the dye and the pigment. And the dye basedink is conventionally used in many cases for the color part from thereason that the outstanding coloring characteristic and stability areacquired.

However, if the recording paper only for the ink jet printing in whichsolidity, such as the light resistance of the image obtained using colorsystem ink and durability, is inferior to the colorant to the thingusing the pigment and which has the ink absorption layer especiallyabout durability is used, although it will become possible to aim at acertain amount of improvement, when the plain paper is used, it iscommon that it is not that which may be satisfactory.

Then, in order to improve the problem over the color system ink in thecase where the plain paper is used in recent years, examination orutilization is carried out for use of the pigment system ink which usesthe organic pigment, the carbon black, etc. as the colorant to the plainpaper printing.

Since the pigment does not have the solubility to the water unlike thecolor, usually, it mixes and carries out the distributed processing ofthe pigment with the dispersant, and is used for the water as water inkin the state where stable dispersion was carried out.

Generally, using the pigment allows the light resistance and waterproofimprovement to be obtained. However, it is difficult to satisfy theother image quality characteristics simultaneously. Especially, it isdifficult to obtain high image concentration, sufficient coloringcharacteristic, color-reproduction characteristic, etc. when carryingout the high-speed printing on the plain paper. There have been stillthe image quality problems that are not fully satisfactory, such as thecharacter blot, the color boundary blot, the double-sided printingcharacteristic, the ink dryness characteristic (fixing characteristic),etc.

A description will be given of the composition of the ink according tothe present invention. The ink drop according to the present inventionemploys the printing ink which has the following composition.

That is, the pigment is used as the colorant for printing, and thesolvent for decomposing and distributing the pigment is used as theindispensable ingredient. And the wetting agents, the surface activeagent, the emulsion, the antiseptics, and the pH adjustment agent arefurther used as the additives. The wetting agent 1 and the wetting agent2 are mixed because viscosity adjustment can be performed easily and therespective features of the wetting agents can be harnessed. Namely, theink according to the present invention is essentially composed of thefollowing elements (1) to (10):

(1) Pigment (self-dispersibility pigment) 6 wt % or more;

(2) Wetting agent 1;

(3) Wetting agent 2;

(4) Water-soluble organic solvent;

(5) Surface active agent of anionic or nonionic type;

(6) Polyol or glycol ether with the carbon number of eight or more;

(7) Emulsion;

(8) Antiseptics;

(9) pH adjustment agent;

(10) Pure water.

Hereafter, each of the elements of the ink according to the presentinvention will be explained.

(1) Concerning the pigment, the inorganic pigment and the organicpigment may be used without limiting the kind of the pigment. Theexamples of the inorganic pigment used may include titanium oxide, ironoxide, and further include the carbon black which is manufactured byusing the well-known methods, such as the contacting method, the furnacemethod, and the thermal method.

Moreover, the examples of the organic pigment used may include the azopigments (for example, azo lake, insoluble azo pigment, condensation azopigment, chelate azo pigment, etc.), the multi-ring type pigments (forexample, phthalocyanine pigment, perylene pigment, perynone pigment,anthraquinone pigment, quinacridone pigment, dioxazine pigment,thioindigo pigment, iso indolinone pigment, quinophtharone pigment,etc.), the dye chelates (for example, the basic dye type chelate, theacid dye type chelate, etc.), the nitro pigments, the nitroso pigments,the aniline black, etc.

According to the preferred embodiment of the invention, any of thesepigments which has a desirable affinity with the water is preferablyused. The grain size of the pigment used is desirably in the range of0.05 to 10 micrometers, and more preferably, 1 micrometer or less, andmost preferably, 0.16 micrometers or less.

The amount of addition of the pigment as the colorant in the ink isdesirably in the range of about 6 to 20% by weight, and more preferablyin the range of about 8 to 12% by weight.

The following are mentioned as the examples of the pigment preferablyused according to the present invention.

The examples of the black pigment used may include the carbon black(C.I. pigment black 7), such as the furnace black, the lamp black, theacetylene black, and the channel black, the metals, such as copper, iron(C.I. pigment black 11), and titanium oxide, and the organic pigments,such as the aniline black (C.I. pigment black 1).

Moreover, the examples of the color pigments may include the C.I.pigment yellow 1 (First yellow G), 3, 12 (Diarylide yellow YT 553D), 13,14, 17, 24, 34, 35, 37, 42 (yellow iron oxide), 53, 55, 81, 83(Permanent yellow HR), 95, 97, 98, 100, 101, 104, 408, 109, 110, 117,120, 138, 153, the C.I. pigment oranges 5, 13, 16, 17, 36, 43, 51, theC.I. pigment red 1, 2, 3, 5, 17, 22 (Brilliant first Scarlett), 23, 31,38, 48:2 (Permanent red 2B (Ba)), 48:2 (Permanent red 2B (calcium)) 48:3(Permanent red 2B (Sr)), 48:4 (permanent red 2B (Mn)), 49:1, 52:2, 53:1,57:1 (Brilliant Carmine 6B), 60:1, 63:1, 63:2, 64:1, 81 (Rhodamine 6Glake), 83, 88,101 (Iron oxide red), 104, 105, 106, 108 (Cadmium red),112, 114, 122 (quinacridone magenta), 123, 146, 149, 166, 168, 170, 172,177, 178, 179, 185, 190, 193, 209, 219, the C.I. pigment violet 1(Rhodamine lake), 3, 5:1, 16, 19, 23, 38, the C.I. pigment blue 1, 2, 15(Phthalocyanine blue R), 15:1, 15:2, 15:3 (Phthalocyanine blue E), 16,17:1, 56, 60, 63, the C.I. pigment greens 1, 4, 7, 8, 10, 17, 18, 36,etc.

In addition, the surface of the pigment (for example, carbon) isprocessed by the resin etc., and the graft pigment which is dispersiblein water, the processed pigment which is dispersible in water with thefunctional groups, such as sulfone group or carboxyl group, which areadded to the surface of the pigment (for example, carbon) may be used.

Moreover, the microcapsule which is made to contain the pigment suchthat the pigment can be dispersed in water may be used.

According to the preferred embodiment of the invention, it is desirablethat the pigment for black ink and the dispersant are added to the inkas the pigment dispersion liquid which is made to disperse the pigmentin the water medium. The desirable example of the dispersant used may bethe known dispersion liquid used for adjusting the known pigmentdispersion liquid.

The examples of the dispersion liquid used may include the following:poly-acrylic acid, poly-methacrylic acid, acrylic acid-acrylonitrilecopolymer, vinyl acetate acrylic acid ester copolymer, acrylicacid-acrylic acid alkyl ester copolymer, styrene acrylic acid copolymer,styrene methacrylic acid copolymer, styrene acrylic acid-acrylic acidalkyl ester copolymer, styrene methacrylic acid-acrylic acid alkyl estercopolymer, styrene-alpha-methyl styrene acrylic acid copolymer, styrenealpha-methyl styrene acrylic acid copolymer-acrylic acid alkyl estercopolymer, styrene maleic acid copolymer, the vinyl-polymers naphthalenemaleic acid copolymer, vinyl acetate ethylene copolymer, vinyl acetatefatty acid vinyl-polymers ethylene copolymer, vinyl acetate maleatecopolymer, vinyl acetate crotonic acid copolymer, vinyl acetate acrylicacid copolymer, etc.

According to the preferred embodiment of the invention, the averagemolecular weight of any of these copolymers used is desirably in therange of 3,000 to 50,000, more preferably, in the range of 5,000 to30,000, and most preferably in the range of 7,000 to 15,000. The amountof addition of the dispersant used may be in such a range that thepigment is dispersed stably without affecting the effects of theinvention. The ratio of the pigment to the dispersant is desirably inthe range of 1:0.06 to 1:3 is desirable, and more preferably in therange of 1:0.125 to 1:3.

The ratio of the pigment used for the colorant to the total weight ofthe printing ink is in the range of 6% to 20% by weight, and the grainsize of the colorant pigment is in the range of 0.05 micrometers to 0.16micrometers. The pigment is dispersed in water, and the dispersant isthe macromolecule dispersant the molecular weight of which is in therange of 5,000 to 100,000. If the water-soluble organic solventcontaining the pyrolidone derivative, especially 2-pyrolidone is usedfor at least one of the color inks, the image quality will improve.

(2) to (4) Concerning the wetting agent 1, the wetting agent 2 and thewater-soluble organic solvent, the water is used as a liquid medium inthe ink. In order to obtain the desired physical properties of the inkand to prevent dryness of the ink, and in order to improve thedissolution stability etc., the examples of the water-soluble organicsolvent used may include the following. It is possible to use thesewater-soluble organic solvents by mixing two or more solvents.

The examples of the wetting agents 1 and 2 and the water-soluble organicsolvent used may include the following: the polyhydric alcohols, such asethylene glycol, di-ethylene glycol, tri-ethylene glycol, propyleneglycol, di-propyrene glycol, tri-propyrene glycol, tetra-ethyleneglycol, hexylene glycol, polyethylene glycol, polypropylene glycol,1,5-pentanediol, 1,6-hexanediol, glycerol, 1,2,6-hexanetriol,1,2,4-butanetriol, 1,2,3-butanetriol, petriol; the polyhydric alcoholalkyl esters, such as ethylene glycol mono-ethyl ether, ethylene glycolmono-butyl ether, di-ethylene glycol mono-methyl ether, di-ethyleneglycol mono-ethyl ether, di-ethylene glycol mono-butyl ether,tetra-ethylene glycol mono-methyl ether, propylene glycol mono-ethylether; the polyhydric alcohol allyl ethers, such as ethylene glycolmono-phenyl ether, ethylene glycol mono-benzyl ether; the nitrogen-including multi-ring compounds, such as 2-pyrolidone,N-methyl-2-pyrolidone, N-hydroxyethyl-2-pyrolidone,1,3-dimethylimidazolidinone, epsilon-caprolactam, gamma-butyrolactone;the amide compounds, such as formamide, N-methyl formamide, N,N-dimethylformamide; the amine compounds, such as mono-ethanol amine, di-ethanolamine, tri-ethanol amine, mono-ethyl amine, di-methyl amine, tri-ethylamine; the sulfur-including compounds, such as di-methyl sulfoxide,sulfolane, thiodiethanol; propylene carbonate, carbonic acid ethylene,etc.

The desirable examples of these organic solvents may include diethyleneglycol, thiodiethanol, polyethylene glycol 200-600, triethylene glycol,glycerol, 1,2,6-hexanetriol, 1,2,4-buthanetriol, petriol,1,5-penthanediol, 2-pyrolidone, and N-methyl-2-pyrolidone. These areeffective in solubility and prevention of the poor injectioncharacteristic due to the moisture evaporation.

The other wetting agents suitably used may contain the saccharide. Theexamples of the saccharide used may include the monosaccharides, thedisaccharide, the oligosaccharides (the trisaccharide andquatrosaccharide are included), and the polysaccharides. The desirableexamples of the polysaccharides may include the glucose, the mannose,the fructose, the ribose, the xylose, the arabinose, the galactose, themaltose, the cellobiose, the lactose, the sucrose, the trehalose, themaltotriose, etc. Here, the polysaccharide means the sugar in the widesense and suppose that it includes the substances which widely exist inthe nature, such as alpha-cyclodextrin, cellulose, etc.

Moreover, the examples of the derivatives of these saccharides mayinclude the reducing sugar (for example, the sugar alcohol (generalformula: HOCH2(CHOH)nCH2OH where n is the integer of 2 to 5), theoxidation sugar (for example, the aldon acid, the uron acid, etc.), theamino acid, the thio acid, etc. Especially the sugar alcohol isdesirable and the desirable examples of the sugar alcohol may includethe Maltitol, the Sorbit, etc.

The content of the saccharides in the ink is desirably in the range of0.1 to 40% by weight, and more preferably in the range of 0.5-30% byweight.

(5) Concerning the anionic or nonionic surface active agent, any agentmay be used without limiting the kind of the surface active agent. Theexamples of the anionic surface active agent used may includepolyoxyethylene alkyl ether acetate, dodecylbenzene sulfonate, lauricacid salt, polyoxyethylene alkyl ether sulfate, etc.

The examples of the nonionic surface active agent may includepolyoxyethylene alkyl ether, polyoxyethylene alkyl ester,polyoxyethylene sorbitan fatty acid ester, polyoxyethylene alkylphenylether, polyoxyethylene alkyl amine, polyoxyethylene alkyl amide, etc.One of the above examples of the surface active agents may be usedsolely or two or more among them may be mixed in combination.

The surface tension according to the present invention is an index whichdenotes the permeability to paper. Specifically, it means the dynamicsurface tension for the short time within one second after the surfaceis formed, and it differs from the static surface tension measured bythe saturation time.

Although any method of measuring the dynamic surface tension, such asthe conventional measuring method which is known from Japanese Laid-Openpatent Application No. 63-31237, can be used, the surface tensionmeasuring instrument of Wilhelmy hung-board type is used to measure thedynamic surface tension according to the present invention.

The desirable value of the surface tension which allows excellent fixingcharacteristic and dryness characteristic is smaller than 40 mJ/m², andmore preferably it is smaller than 35 mJ/m².

(6) Concerning the polyol or glycol ether with the carbon number ofeight or more, the polyol and/or glycol ether which is partiallywater-soluble and has the solubility in a range of 0.1 to 4.5% by weightin water at 25-degree C. is added so that the ratio of the content ofthe polyol and/or glycol ether to the total weight of the printing inkis in the range of 0.1 to 10.0% by weight. It is turned out that if theabove conditions are met, the wettability to the heat element of the inkis improved and the discharge stability and frequency stability areacquired with a small amount of addition.

(6-1) 2-ethyl-1,3-hexanediol; solubility:4.2% (20 degrees C.)

(6-2) 2,2,4-trimethyl-1,3-pentanediol; solubility: 2.0% (25 degrees C.)

The penetrant which has the solubility in the range of 0.1 to 4.5% byweight in water at 25-degree C. is advantageous in that the permeabilityis high in spite of low solubility. Therefore, it is possible to producethe ink which has high permeability, with the other solvent incombination with the penetrant having the solubility in the range of0.1-4.5% by weight in water at 25-degree C., or in combination with theother surface active agent.

(7) Concerning the emulsion, it is desirable that the resin emulsion beadded to the ink according to the present invention. The resin emulsionmeans the emulsion whose continuation phase is the water and whosedispersion phase is one of the following resin ingredients. The examplesof the resin ingredients of the dispersion phase of the resin emulsionused may include the acrylic resin, the vinyl acetate resin, thestyrene-butadiene resin, the vinyl chloride resin, the acrylic styreneresin, the butadiene resin, the styrene resin, etc.

According to the preferred embodiment of the invention, it is desirablethat the resin is the polymer having both the hydrophilic portion andthe hydrophobic portion.

Moreover, although the grain size of the resin is not limited as long asthe emulsion is formed, the desirable diameter of the grain of the resinis about 150 nm or less, and more preferably is in the range of 5 to 100nm. In these resin emulsions, the resin particles can be obtained bymixing in the water with the surface active agent in some case.

For example, the emulsion of the acrylic resin or the styrene-acrylicresin can be obtained by mixing (meta)acrylic acid ester and the surfaceactive agent with (meta)acrylic acid ester or styrene, and in some case(meta)acrylic acid (meta)ester in the water.

The rate of mixture with the resin ingredients and the surface activeagent is desirably in the range of 10:1 to 5:1. The formation of theemulsion becomes difficult when the amount of the surface active agentused does not reach the range. On the other hand, when the amount of thesurface active agent used exceeds the range, the durability of the inkfalls or there is the tendency for permeability to get worse.

The rate of the weight parts of the water to 100 weight parts of theresin in the dispersion phase of the resin emulsion is desirably in therange of 60 to 400, and more preferably in the range of 100 to 200. Theexamples of the commercially available resin emulsions may include“maikuro-jeru” E-1002 and E-5002 (styrene acrylic resin emulsion, NipponPaint Co., Ltd.), “bonkohto” 4001 (acrylic resin emulsion, Dainippon Ink& Chemicals Inc.), “bonkohto” 5454 (styrene acrylic resin emulsion,Dainippon Ink & Chemicals Inc.), SAE-1014 (styrene acrylic resinemulsion, Nippon Zeon Co., Ltd.), “saibinohru” SK-200 (acrylic resinemulsion, Saiden Chemistry Co., Ltd.), etc.

In the ink used according to the present invention, the ratio of thecontent of the resin ingredients of the resin emulsion to the ink isdesirably in the range of 0.1-40% by weight, and more preferably in therange of 1-25% by weight.

The resin emulsion has the character thickened and condensed, inhibitsthe osmosis of the coloring ingredients, and further has the effectwhich promotes fixing to the printing medium.

Moreover, depending on the kind of resin emulsion, the coat is formed onrecord material, and it has the effect which also raises the frictionresistance of the printed matter.

(8) to (10) The known additives in the art, other than the colorant, thesolvent, and the surface active agent, can be added to the ink accordingto the present invention.

The examples of the antiseptics or antimold used may includedehydroacetic acid sodium, sorbic acid sodium, 2-pyridinethiol-1-oxidesodium, benzoic acid sodium, pentachlorophenol sodium, etc.

Concerning the pH adjustment agent, any arbitrary substances can be usedif the pH value of the ink can be adjusted to be seven or more withoutaffecting the ink prepared. The examples of the pH adjustment agent usedmay include the amines, such as diethanol amine and triethanol amine,the carbonates of alkali metals, such as lithium carbonate, sodiumcarbonate and potassium carbonate, the hydroxides of alkali metals,lithium hydroxide, sodium hydroxide, potassium hydroxide, ammoniumhydroxide, the 4th class ammonium hydroxide, the 4th class phosphoniumhydroxide, etc.

The examples of the chelating reagent used may includesethylene-diamine-tetraacetic acid sodium, nitrilo-triacetic acid sodium,hydroxyethyl ethylenediamine-triacetic acid sodium,diethylene-triamine-pentaacetic acid sodium, uramildiacetic acid sodium,etc.

The examples of the anticorrosive used may include acid sulfite, sodiumthiosulfate, ammonium thiodiglycolate, diisopropylamine nitrite,pentaerythritol tetranitrate, dicyclohexylamine nitrite, etc.

Next, the examples of the dots printed by the ink-jet printing devicewill be explained with reference to FIG. 6 to FIG. 8.

FIG. 6 shows the example of the output character which is subjected tothe conventional half-tone processing using 50% for each of the largeand middle drops. FIG. 7 shows the dot configuration of the slantingline part which is subjected to the conventional half-tone processingusing 50% for each of the large and middle drops.

As shown in FIG. 6, in this example, jaggies take place in the slantingline part of the character, which shows a poor character quality. Thisis because, as shown in FIG. 7, the dots in the slanting line part arearranged in the shape of stairs.

In this example, the number of the dots which form the straight linebetween the two step-change parts of the stair-like character portion isfour (which is called the one-fourth inclination slanting).

On the other hand, FIG. 8 shows the dot configuration of the slantingline part which is subjected to the half-tone processing in thepreferred embodiment of the invention which uses 50% for each of thelarge drop and the middle drop (which corresponds to the example of FIG.7), and FIG. 8(a) to (d) show different jaggies correction methods.

In FIG. 8(a) and (b) indicate the examples in which the small drop isadded to the blank part at the changing point, and (c) and (d) indicatethe examples in which the small drop is added to the blank part andfurther the image dot is replaced by the small drop.

Specifically, FIG. 8(a) shows the example in which one small drop isadded to the blank part (positions of 46 and 51) at the changing point.The small drop is printed at the blank part 46 of the changing point.FIG. 8(b) shows the example in which two small drops are added to theblank part (positions of 46, 45, 51, and 52) at the changing point. Thetwo small drops are printed at the blank parts 45, 46, 51, and 52 of thechanging points.

FIG. 8(c) shows the example in which the dots (dots of 47 and 50) whichform the changing point are replaced by the small drops in addition tothe example of FIG. 8(b). The small drops are printed at the two blankparts and the one image part (45, 46, 47, 50, 51, 52) of the changingpoints.

FIG. 8(d) shows the example in which the two dots (48, 49) which formthe changing point are further replaced by the small dots in addition tothe example of FIG. 8(c).

In these examples, the step-change part of the shape of stairs of thechanging point is formed by the small drops, and the slanting line partis made comparatively smooth by the composition of the dots only.Furthermore, the ink-jet printer has the characteristics that the inkafter reaching the paper spreads. Moreover, when the ink containing thecoloring agent as the major components is printed on the plain paper isused, the problem called feathering arises even if jaggies are improvedby the composition of the dots.

By using the ink of the present invention for the ink jet printing, theproblem of feathering etc. can be reduced, and the blot of the shape ofa mustache is lost and the improvement effect by the composition of thedots can be effectively raised.

Furthermore, according to the ink of the present invention, thefeathering is reduced but the overall blot remain in some content. Inassociation with the surrounding dots, the outline part of the dotsbecomes smooth, and it is possible that the presence of jaggies in theoutput character becomes less conspicuous.

Therefore, it is possible to make jaggies hardly conspicuous by formingthe smooth slanting part, although jaggies are the phenomenon peculiarto the ink jet printing, and still more peculiar to the ink of theinvention.

In addition, in the present embodiment, the above description has beengiven of the half-tone processing of the ratio of 50% for each of thelarge drop and the middle drop. Similarly, the half-tone processingwhich uses the large drop and the middle drop can be carried out for allthe cases of any arbitrary ratio of the large drop and the middle drop.

Moreover, the above description has been given of the one-fourthinclination slanting in this embodiment. The same processing can beperformed similarly for the other slanting with inclination of 1/3, 1/5or less, and the slanting line subjected to mirroring or to rotation of270 degrees, 180 degrees or 90 degrees.

FIG. 19(a) shows the case in which the number of the dots which form thestraight line between two step-change parts in the slanting line whichis subjected to half-tone processing using 50% for each of the middleand small drops is 4 (slanting of inclination 1/4).

As shown in this example, the step-change part of the shape of stairs ofthe changing point is reduced by forming the small drop, and thecomparatively smooth slanting line part can be formed by the compositionof the dots only. Furthermore, the ink-jet printer has thecharacteristics that the ink after reaching the paper spreads. Moreover,when the ink containing the coloring agent as the major components isprinted on the plain paper is used, the problem called feathering ariseseven if jaggies are improved by the composition of the dots.

By using the ink of the present invention for the ink jet printing, theproblem of feathering etc. can be reduced, and the blot of the shape ofa mustache is lost and the improvement effect by the composition of thedots can be effectively raised.

Furthermore, according to the ink of the present invention, thefeathering is reduced but the overall blot remain in some content. Inassociation with the surrounding dots, the outline part of the dotsbecomes smooth, and it is possible that the presence of jaggies in theoutput character becomes less conspicuous.

Therefore, it is possible to make jaggies hardly conspicuous by formingthe smooth slanting part, although jaggies are the phenomenon peculiarto the ink jet printing, and still more peculiar to the ink of theinvention.

Moreover, the method of adding two small drops to the blank part(positions of 46, 45, 51, 52) of the changing points will allow the sameeffect. Furthermore, if the dot (dots of 47 and 50) which forms thechanging point is replaced by the small drop, and the two small dropsare printed at two blank parts of the changing point and one image part(45, 46, 47, 50, 51, 52), the same effect can be obtained. Moreover, ifthe two (48, 49) of the dots which forms the changing point aretransformed into the small drops and the two small drops are printed attwo blank parts of the changing point and two image parts (45, 46, 47,50, 51, 52), the same effect can be obtained.

In addition, in the present embodiment, the above description has beengiven of the case of the half-tone processing which uses the ratio of50% for each of the small drop and the middle drop. The half-toneprocessing can also be carried out similarly in the case of the ratioused as the middle drop>small drop. That is, in such a case, the numberof the middle drops used is larger than the number of the small dropsused.

Moreover, in the present embodiment, the above description has beengiven of the slanting line with the one-fourth inclination. The samediscussion is applicable to the other slanting lines with a differentinclination similarly, and also to those subjected to mirroring of thesame and those rotated by 270 degrees, 180 degrees or 90 degrees.

Furthermore, the case in which the number of the dots which form thestraight line between two step-change parts (F, G) in the slanting linewhich performed half-tone processing which uses the ratio of 50% foreach of the large and middle drops is 2 (the slanting line with 1/2inclination) is shown in FIG. 15(a).

In this case, if the two drops of small drops are added to the blank ofthe changing point, it can add to the same position (namely, the nextchanging point) as the image dot which forms the slanting line, and thestairs-like image cannot be improved (b).

Then, in the present invention, in order to solve this, in such a case,it is supposed that it is about the addition range of the small drop tothe 1-pixel this side of the changing point (namely, number-1 of the dotwhich forms the straight line between step-change parts) (c).

The slanting which inclined by this and has improved jaggies also withone half of the slanting line comes to be obtained.

In addition, although this embodiment described the case in half-toneprocessing of the ratio of 50% of each of the large and middle drops, inthe half-tone processing which uses the large and middle drops, all canbe similarly carried out about the case of the ratio of the large andmiddle srops, and the case of the ratio which serves as the middledrop>=small drop by the half-tone processing which used the minor drop.That is, it can carry out similarly about the case where the number ofthe dots of the middle drop is larger than the number of the dots of thesmall drop.

Furthermore, the example in case the number of the dots which form thestraight line between two step-change parts in the slanting line whichperformed half-tone processing which includes the 50% of each of thelarge and middle drops with FIG. 16 is 1 (slanting of inclination 1/1)is shown (a).

In this case, if the small drop is added, it will become the sameslanting as the image dot which forms the slanting line, and the widthof the line will become thick.

In the present invention, in order to solve this, when jaggies cannot beconspicuous easily since the stairs-like portion continues, and 1/1 ofthe slanting line are the ink-jet printers from the first, in the eyethe card game and such a case, the small drop is not added to thetendency for the stairs-like portion to be relaxed by the spread of theink and the blot of some it is made like (number-1=0 of the dot which inother words forms the straight line between step-change parts).

The undesired influence by this inclining and carrying out jaggiesaddition with 1/1 of the slanting line can be lost.

In addition, although this embodiment described the case in half-toneprocessing of the ratio of 50% of each of the large and middle drops, inthe half-tone processing which uses the large and middle drops, all canbe similarly carried out about the case of the ratio of the large dropand the middle drop, and the case of the ratio which serves as themiddle drop>=small drop by the half-tone processing which used the minordrop.

That is, it can carry out similarly about the case where the number ofthe dots of the middle drop is larger than the number of the dots of thesmall drop.

Furthermore, the example in case the number of the dots which form thestraight line between two step-change parts in the slanting line whichperformed half-tone processing which includes the 100% of small dropswith FIG. 18 is 4 (slanting of inclination 1/4) is shown (a).

In this case, if the small drop is added, it cannot become the sameslanting as the image dot which forms the slanting line, and thestairs-like image cannot be improved.

In the present invention, since the slanting line which includes smalldrops from the first in order to solve this has low concentration,jaggies cannot be conspicuous easily, and when it is the ink-jetprinter, in the eye the card game and such a case, it does not add thesmall drop to the tendency for the stairs-like portion to be relaxed bythe spread of the ink and the blot of some.

The unnecessary load to the host computer by carrying out jaggiesaddition with the slanting line which performed half-tone processingwhich includes the 100% of small drops by this similarly can be lost.

In addition, although this embodiment described the slanting line whichperformed half-tone processing which includes the 100% of small drops,the ratio of the small and middle drops in half-tone processing.

It can carry out similarly about the case where it becomes the middledrop<small drop. That is, it can carry out similarly about the casewhere there are more dots of the small drop than the number of the dotsof the middle drop.

In the present embodiment, the above description has been given of theslanting line with the one-fourth inclination. However, the samediscussion is applicable to other slanting lines with a differentinclination similarly, and also to those subjected to mirroring of thesame and those rotated by 270 degrees, 180 degrees or 90 degrees.

As mentioned above, the optimal jaggies correction for each respectiveinclinations can be attained by selecting one of the different jaggiescorrection methods according to the inclination of the slanting line orthe level of gradation of the half-tone processing.

Next, a description will be given of a method of forming the small dropto the changing point of the step-change part of the image outline.

As a method of adding or replacing the small drop, pattern matching isused as an excellent method. FIG. 20 shows the example of the windowused for pattern matching. This window is provided with the size ofwidth m and length n (m×n). The following explanation will be given forthe case in which the window size of m=5 and n=5 is used (FIG. 11).

The font data which is not yet subjected to half-tone processing isdeveloped to bitmap data by the printer driver software. This bitmapdata represents the dots which form the font. Pattern matching iscarried out for each bit of the bitmap data derived from the font dataon the basis of the size of the above-mentioned window.

FIG. 12 is a flowchart for explaining the processing of the patternmatching described above.

First, it is determined whether the ratio of the small drop used in thehalf-tone processing is 50% or more. If the result is affirmative, theprocessing ends. If the result is negative, the control is transferredto next step.

Next, the target pixel is set at the starting position of font databefore the half-tone processing. By taking into consideration the targetpixel, the bitmap data of the font data equivalent to the window isacquired. In this case, the acquired bitmap data is the dot data for 25(=5×5) dots.

Next, the pattern matching is performed so that the acquired data iscompared with the data of the predetermined pattern (called thereference pattern) which is used to add or replace the small drop. Whena match in the pattern matching occurs, the target pixel is replaced bythe data indicating the small drop. The processing may be performed suchthat one pixel is represented by one byte of the data or one bit of thedata.

When one pixel is represented by one byte, 25 bytes of the data areneeded to express the data for 25 dots. When one pixel is represented byone bit, only the amount of data of 4 bytes is needed to express thedata for 25 dots (when the processing is performed only for the dataother than the target pixel, only the data of 3 bytes is need), theamount of the data being processed is smaller for the case of the 1-bitdata processing. Since saving of the memory and improvement of theprocessing speed can be attained, the latter method is desirable.

FIG. 14 shows the details of the processing of the pattern matching. Itis in the state of the window when FIG. 14(a) makes 46 of font data asthe reference pattern and (b) makes it the target pixel. Since thepattern of both dot is in agreement, the position of the target pixel 46is replaced by the small drop from the blank (c).

The data in which the small drop is shown in the creation of small dropdata. When the original font data is expressed with 0 (blank) and 255(printing data) like bitmap data, or when are expressed with the twovalues like 0 (blank) and 1 (printing data) and it once transforms like0 (blank) and 255 (printing data), you may replace the data itself whichforms blank data and the font by the data (for example, respectively 85)showing the small drop.

Moreover, what is necessary is to prepare the memory (memory for smalldrop data), and just to create 1 which expresses printing data toposition where the same size as font data is another, and which attachesthe small drop in it, when processing with 0 and 1.

The slanting with which jaggies like FIG. 8 have been improved isrealizable by printing (the case of the latter), the small drop, and thelarge drop by the font data (in the case of the former) which consistedof the data in which the small drop which created by pattern matching,and the large drop are shown or the binary (0 1) data for small drops,and the original the binary (0 1) font data.

By using the window and reference pattern of 5×5, judgment whether itreplaces by the small drop to the blank of the 2 dots and the image dotapproximately focusing on the changing point is attained.

For example, the position of 45 can replace by the small drop with thereference pattern of FIG. 17(a). The dot of 48 is similarly replaced for47 by the small drop by FIG. 17(b) by (c).

It is because the reason which can be carried out cannot detect thechanging point by receiving the 2 dots before and after the changingpoint since the changing point is judging the target pixel out of thewindow in the position of for example, FIG. 14 window.

In canceling this and adding the suitable small drop, it becomespossible by making the window and the reference pattern into the size of7×7.

That is, by enlarging the size of the window, and the size of thereference pattern, the changing point of the level or perpendicularlynear slanting can be detected, it becomes possible to add the small dropaccording to the inclination, and those slanting quality can be mademuch more the optimal.

That is, it is decided by how far the size of the window and thereference pattern needs to carry out displacement not only to what isused in this embodiment but the small drop, or whether processing timedoes to printing velocity.

Since the data which carries out pattern matching will become large ifit furthermore says, and this size becomes large, the pattern matchingis time consuming. Therefore, from processing time, the smaller possibleone as the size is desirable.

On the other hand, before and after the changing point, since it isdecided in how many dots whether the small drop should be carried outfrom the character quality by jaggies correction, it is necessary todetermine the optimal size as processing velocity from characterquality.

When the above ink was used by the experiment of the present-inventionperson, as for reduction of unevenness with the contiguity dot by thespread of the ink, it turns out also by small drop addition of the 7 orless dots that improvement in character quality can be aimed at enough,and processing velocity also showed that the throughput 10 ppm or morecould be attained. Therefore, as the size of the window, the size ofm<=7 or n<=7 is suitable.

Moreover, when the window of the same size is used, about the point ofprocessing velocity to the embodiment (FIG. 8(a)-(e)), FIG. 8(a) are thequickest and become late in order of (b), (c), (d), and (e).

The processing method compares what to perform pattern matching to one,only when the target pixel is blank and (a) and (b) is (c) image dots,and this is the case where it is blank in (d) and (e), and in the caseof both the image dot (that is, it is because all font data needs toperform pattern matching). In other words, the font data which hasimproved jaggies at high speed can be created by accepting it blank andadding the small drop.

Moreover, the font data which has improved jaggies at high speed can becreated by replacing only the image dot by the small drop.

As the second, the number of required reference patterns is forincreasing in order of (a), ((b)=(c)), (d), and (e). In order to carryout (b), this needs the reference pattern which judges the second dot ofthe blank further for the reference pattern of (a), and the referencepattern which judges the first dot further is required for it in (d),and it is because the reference pattern for judging the second dotfurther is needed in (e).

Here, how to perform small drop addition processing only to the dotwhich forms the image for how FIG. 21 performs addition processing ofthe small drop only in the blank part with FIG. 22 is described.

How to add the small drop only to the blank part is described. Theflowchart is shown in FIG. 21.

First, the target pixel is set at the starting position of font data.The image data to the target pixel is seen and the data (data ofwhich=printing is done) with which the data forms the blank data or thefont is judged.

Subsequently, the following pattern matching is carried out only at thetime of the data in which the blank is shown, and, in the case of thedata which forms the font, the changing point by pattern matching is notdetected.

Since time to carry out pattern matching by this by the data which formsthe font is lost, improvement in processing velocity can be aimed at.

The bitmap data of the font data equivalent to the window is acquiredfocusing on the target pixel at the time of the data in which the blankis shown. Therefore, the acquired bitmap data is the data for the 25dots of 5×5.

When the acquired data is compared with the data of the pattern(henceforth the reference pattern) which adds or replaces the small dropset up beforehand and being matched by pattern matching, the targetpixel is replaced by the data in which the small drop is shown.

These processings may treat the 1 pixel as the 1 byte of the data, andmay treat it as the 1-bit data. When treating as the 1-bit data to the25 bytes being required expressing the data for the 25 dots whentreating as the 1 byte of the data.

Since it ends with the amount of data of the 4 bytes (it is desirable atthe 3 bytes when carrying out only to the data other than the targetpixel) to express the data for the 25 dots, the number of the data whichthe way treated as the 1-bit data processes is small, and since savingof the memory and improvement in processing velocity can be aimed at, itis desirable.

FIG. 14 explains the example of pattern matching still in detail.

It is in the state of the window when FIG. 14(a) makes 46 of font dataas the reference pattern and (b) makes it the target pixel. Since thepattern of both dot is in agreement, the position of the target pixel 46is replaced by the small drop from the blank (c).

By using the window and reference pattern of 5×5, judgment whether thesmall drop is added to the image dot of the blank 2 which adjoins thechanging point is attained.

Next, how to replace only the data (=printing data) which forms the fontby the small drop is described.

The flowchart is shown in FIG. 22. First, the target pixel is set at thestarting position of font data.

The image data to the target pixel is checked, and it is determinedwhether the data forms the blank or the font (printing data).

Subsequently, the following pattern matching is carried out only at thetime of the data which forms the font, and, in the case of the datawhich forms the blank, the changing point by pattern matching is notdetected. Since time to carry out pattern matching by this by the datawhich forms the blank is lost, improvement in processing velocity can beaimed at.

The bitmap data of the font data equivalent to the window is acquiredfocusing on the target pixel at the time of the data in which the blankis shown. Therefore, the acquired bitmap data is the data for the 25dots of 5×5.

When the acquired data is compared with the data of the pattern(henceforth the reference pattern) which adds or replaces the small dropset up beforehand and being matched by pattern matching, the targetpixel is replaced by the data in which the small drop is shown.

These processings may treat the 1 pixel as the 1 byte of the data, andmay treat it as the 1-bit data. When treating as the 1-bit data to the25 bytes being required expressing the data for the 25 dots whentreating as the 1 byte of the data.

Since it ends with the amount of data of the 4 bytes (it is desirable atthe 3 bytes when carrying out only to the data other than the targetpixel) to express the data for the 25 dots, the number of the data whichthe way treated as the 1-bit data processes is small, and since savingof the memory and improvement in processing velocity can be aimed at, itis desirable.

FIG. 14 explains the example of pattern matching still in detail. It isin the state of the window when FIG. 14(d) makes 47 of font data as thereference pattern and (e) makes it the target pixel.

Since the pattern of both dot is in agreement, the position of thetarget pixel 47 is replaced by the data in which the small drop is shownfrom the printing data in which the large drop is shown (f).

By using the window and reference pattern of 5×5, judgment whether itreplaces by the small drop to the dot which shows two font data whichadjoins the changing point is attained.

FIG. 23 and FIG. 24 show another embodiment.

Pattern matching is carried out for each bit per the window to thebitmap data as font data.

The flowchart is shown in FIG. 23. First, the target pixel is set at thestarting position of font data.

Focusing on the target pixel, the bitmap data of the font dataequivalent to the window is acquired. Therefore, the acquired bitmapdata is the data for the 25 dots of 5×5.

When the acquired data is compared with the data of the pattern(henceforth the reference pattern) which adds or replaces the small dropset up beforehand and the middle drop and being matched by patternmatching, the target pixel is replaced by the data in which the smalldrop and the middle drop are shown.

These processings may treat the 1 pixel as the 1 byte of the data, andmay treat it as the 1-bit data.

When treating as the 1-bit data to the 25 bytes being requiredexpressing the data for the 25 dots when treating as the 1 byte of thedata. Since it ends with the amount of data of the 4 bytes (it isdesirable at the 3 bytes when carrying out only to the data other thanthe target pixel) to express the data for the 25 dots, the number of thedata which the way treated as the 1-bit data processes is small, andsince saving of the memory and improvement in processing velocity can beaimed at, it is desirable.

When the data in which the small drop and the middle drop are shown isexpressed with 0 (blank) and 255 (printing data) like bitmap data in theoriginal font data at this time, or when are expressed with the twovalues like 0 (blank) and 1 (printing data) and it once transforms like0 (blank) and 255 (printing data), it is possible to replace by the data(for example, respectively 85,170) showing the data itself small dropwhich forms blank data and the font, and the middle drop.

Moreover, what is necessary is to prepare two or more (in the case ofthis embodiment, for it to be two for the object for small drops, andmiddle drops, since it is the two kinds, the small drop and the middledrop) memories with the same another size as font data, and just tocreate 1 which expresses printing data to the position which attachesthe small drop of each inside, and the middle drop, when processing with0 and 1.

With the font data (in the case of the former) which consisted of thedata in which the small drop which created by pattern matching, themiddle drop, and the large drop are shown or the binary (0 1) data forsmall drops, the binary (0 1) data for middle drops, and the originalfont data (two values).

The slanting with which jaggies as shown in FIG. 24 have been improvedis realizable by printing the small drop, the middle drop, and the largedrop.

In addition, although FIG. 24 showed the embodiment in the gradation of100% of large drops, in the half-tone processing which used the Onakadrop, all can be similarly carried out about the case of the ratio ofthe Onaka drop, and the case of the ratio which serves as the middledrop>=small drop by the half-tone processing which used the minor drop.That is, it can carry out similarly about the case where the number ofthe dots of the middle drop is larger than the number of the dots of thesmall drop.

Next, how to change the correction method by inclination is described.

It is chosen whether the present invention changes the target pixel intothe small drop or the middle drop by pattern matching with font data ornothing is carried out. Therefore, it is prepared even for largeinclination from inclination small as a pattern to refer to.

Then, what is necessary is just to change the information into what thetarget pixel is changed, by the pattern in the case of being larger than1/1, and the pattern of the case of 1/1 or less.

This method is described in more detail with reference to FIG. 27.

FIG. 27 is an example of inclination 4/1 (FIG. 27(a)) and the referencepattern of 1/4 (FIG. 27(b)).

When carrying out pattern matching of the font data and being matched bydividing the reference pattern into the reference pattern for the smalldrop transformation, the reference pattern for middle drops, and thereference pattern that further nothing carries out, and carrying outpattern matching by each, it turns out whether transform the targetpixel into the dot of which size, i.e., into which dot data does ittransform.

In the example of FIG. 27, it is that the pattern of (a) uses the middledrop and the pattern of (b) as the transformation pattern of the smalldrop, and transforms into the small drop at the time of the middle dropand inclination 1/4 at the time of inclination 4/1.

Creation of these font data is carried as software called printer driversoftware on PC for sending the image data to the ink-jet printingdevice, as mentioned above. Therefore, it is preserved as the softwarewhich described the jaggies correction unit at the hard disk of the hostcomputer on CDROM or the network, and operation becomes possible witheach PC by installing it.

Moreover, there is also the method of carrying the detection unit in theink-jet printing device itself as another form. When creating bitmapdata from the alphabetic code which entered as this method using CPU,for example by putting in the reference pattern for performing theprocessing method of the jaggies correction, and pattern matching to theprogram stored in ROM in the case of the firmware which consisted of theROMs in which the program for moving CPU and it as shown in FIG. 28 wasstored, what is necessary is just made to carry out the jaggiescorrection.

In this case, since detection of the step-change part of the outlinepart is performed by CPU, CPU serves as the detection unit.

Moreover, as another method, realizing only by hardware is also possiblewithout using CPU.

By doing in this way, about bitmap, since the data transmission betweenPC and the inkjet printer is desirable without using the data, itbecomes the high speed, and improvement in the throughput can be aimedat.

Next, how to print the font data which carried out in this way and wascreated in the record paper by the ink-jet printing device is described.

FIG. 9 is a diagram for explaining the drive waveform of the printinghead. FIG. 10 shows the example of the composition of the drivingcircuit of the printing head (which corresponds to the head driving unit24 of FIG. 4). FIG. 13 shows the example of the composition of thedriver IC.

In the data-processing unit 27 of FIG. 4, and the printing control unit23, the font data as printing data corresponded up to the row of thehead, the creation of 2-bit drive data required in order to havedesirable control of striking the large drop, the small drop, and thethree non-printing values in any direction is performed, and thehorizontal transformation and the head are sent to the head drivecircuit according to the drive periodicity of the head as drive data S2.

Therefore, as drive data, it becomes the number twice the number of thebits of the channels. As a signal sent to the head drive circuit, inaddition, the latch signal S1 for retaining in the latch circuit 61,when it is nothing in the shift register with clock signal S3 forshifting drive data by shift register 60 in driver IC data is assembledthe number of the channels. The drive wave pulsing signal (M1-M3) forchoosing the drive wave corresponding to the dot (large drop) of thesize which forms the image dot for the drive wave, and the drive wavecorresponding to the small drop is sent.

On the other hand, transform into the analog signal the drive wave data(digital signal) which the drive wave forms from CPU by the D/Aconverter as a drive wave creation part which creates the drive wave,and pass further the current amplification machine for supplying enoughthe amplification machine which amplifies this to actual drive voltage,and the current by the drive of the head the drive wave like FIG. 9 isinputted into pinch off voltage of the driver IC.

In the driver IC, according to drive data, one of the drive wave pulsingsignals (M1-M3, logic signal) is chosen by the data selector 62, and itis inputted into the gate of the transmission gate 64 which is theswitching unit through the level shifter 63 which transforms the logicsignal into the drive voltage level.

Therefore, the transmission gate will be switched according to thelength of the selected drive wave pulsing signal, and the wave for smalldrops (a) as shown in FIG. 9, and the wave for large drops (c) will beoutputted to the output terminal (the driver IC of this embodiment13-1-192/).

Moreover, in this embodiment, the drive wave further for middle drops(b) can be chosen now. According to these waves, PZT drives and can havedesirable control of striking the small drop and the large drop in anydirection.

In this embodiment, since the object for small drops and the wave forlarge drops are created from one drive wave, the circuit and signal linewhich supply the drive wave are desirable at one, and theminiaturization of cost reduction, the circuit board, and thetransmission line can be attained.

Thus, the font data to which the small drop is added is actually printedon the plain paper with the ink-jet head on the conditions that aregiven in the following, and the character quality has been evaluated.

-   Head: 384 nozzles/color; nozzle pitch=84 micrometer (equivalent to    300 dpi)-   Image resolution: 300 dpi-   Dot size: 120 micrometers of large drops, 40 micrometers of small    drops-   Characters: MS Mincho; font size=6, 10, 12, 20, 30, 50 or 80 points-   Half-tone processing: 50% for each of the large and middle drops,    50% for each of the middle and small drops-   The jaggies correction method: varied by the slanting part    inclination (refer to Table 1 below)-   Printing method: the number of the paths (the number of scanning    lines to form one line)=1; the interlace=none

Paper: Ricoh MyPaper TA TABLE 1 Slanting Part Jaggies CorrectionInclination: Method: 1/1 No correction 1/2, 2/1 FIG. 15 (c) 1/3, 3/1FIG. 8 (e)

The evaluation of character quality is made by the comparison of thecharacter which is subjected to the jaggies correction method describedabove, the character (comparative example 1) which is not subjected tothe jaggies correction method completely (i.e., the character printedonly with the large drops), and the character (comparative example 2)which is subjected to the correction method of FIG. 8(e) regardless ofthe inclination.

Consequently, the character subjected to the jaggies correction methodof the present invention shows the best character quality. Thecomparative example 2 shows the second best character quality and thecomparative example 1 shows the worst character quality.

Moreover, according to the preferred embodiment of the invention, nofeathering takes place and the character with sufficient imageconcentration can be obtained.

In the present embodiment, the above description has been given of theexample when printed on the plain paper. Alternatively, when printed onthe coated paper, the calendered paper, the OHP film, etc., the sameeffects of the invention can be acquired by applying the imageprocessing of the invention. Moreover, it is possible to select theexecution of the jaggies correction method depending on the type of thepaper used.

Moreover, in the present embodiment, the above description has beengiven of the example in which the character is printed by 300 dpi. Thediameter of the dot which constitutes the character becomes large whenthe character is printed at a low resolution of 200 dpi or 150 dpi, andthe stairs-like step-change part is further conspicuous. In suc a case,the above embodiment can be applied suitably and the effects of theinvention can be also obtained.

However, when the character is printed at a high resolution of 600 dpi,1200 dpi or 2400 dpi, the number of the dots which constitute the fontis large and the dot size becomes small, thus jaggies are notconspicuous. Therefore, in the case of the ink-jet printer which has twoor more printing modes with different printing resolutions, it isdesirable to prepare the mode in which the jaggies correction method ofthe invention is carried out, and the mode in which such is not carriedout, and to choose one of the two modes according to the resolution, forthe purpose of improvement in the throughput.

As a standard of the resolution, generally at the printing resolution of450 dpi or more, the character quality in which jaggies are notconspicuous is obtained. Hence, in the case of the printing resolutionof 450 dpi or more, it is desirable not to carry out the jaggiescorrection method of the invention. On the other hand, in the case ofthe printing resolution of 360 dpi or less, it is desirable to carry outthe jaggies correction method of the invention. In other words, theprocessing time can be shortened by detecting the changing point only inthe case of the printing resolution of 360 dpi or less.

Furthermore, another example will be given below. The font data to whichthe small drop is added is actually printed on the plain paper with theink-jet head on the conditions that are given in the following, and thecharacter quality has been evaluated.

-   Head: 384 nozzles/color; nozzle pitch=84 micrometers (equivalent to    300 dpi)-   Image resolution: 300 dpi-   Dot size: 120 micrometers of large drops, 70 micrometers of middle    drops, and 40 micrometers of small drops-   Character font: MS Mincho; font size=6, 10, 12, 20, 30, 50 or 80    points-   Half-tone processing: 50% for each of the large drop and the middle    drops; 50% for each of the middle drop and the small drop-   The jaggies correction method: varied depending on the slanting part    inclination (refer to Table 2 below).-   Printing method: the number of the paths (the number of scanning    lines to form one line)=1; the interlace=none

Paper: Ricoh MyPaper TA TABLE 2 Slanting Part Jaggies CorrectionInclination: Method: 1/1 No correction 1/2, 2/1 FIG. 15 (c) 1/3, 3/1FIG. 24 (e)

The evaluation of character quality is made by the comparison of thecharacter which is subjected to the jaggies correction method describedabove, the character (comparative example 1) which is not subjected tothe jaggies correction method completely (i.e., the character printedonly with the large drops), and the character (comparative example 2)which is subjected to the correction method of FIG. 8(e) regardless ofthe inclination.

Consequently, the character subjected to the jaggies correction methodof the present invention shows the best character quality. Thecomparative example 2 shows the second best character quality and thecomparative example 1 shows the worst character quality.

Moreover, according to the preferred embodiment of the invention, nofeathering takes place and the character with sufficient imageconcentration can be obtained.

In the present embodiment, the above description has been given of theexample when printed on the plain paper. Alternatively, when printed onthe coated paper, the calendered paper, the OHP film, etc., the sameeffects of the invention can be acquired by applying the imageprocessing of the invention. Moreover, it is possible to select theexecution of the jaggies correction method depending on the type of thepaper used.

Moreover, in the present embodiment, the above description has beengiven of the example in which the character is printed by 300 dpi. Thediameter of the dot which constitutes the character becomes large whenthe character is printed at a low resolution of 200 dpi or 150 dpi, andthe stairs-like step-change part is further conspicuous. In suc a case,the above embodiment can be applied suitably and the effects of theinvention can be also obtained.

However, when the character is printed at a high resolution of 600 dpi,1200 dpi or 2400 dpi, the number of the dots which constitute the fontis large and the dot size becomes small, thus jaggies are notconspicuous. Therefore, in the case of the ink-jet printer which has twoor more printing modes with different printing resolutions, it isdesirable to prepare the mode in which the jaggies correction method ofthe invention is carried out, and the mode in which such is not carriedout, and to choose one of the two modes according to the resolution, forthe purpose of improvement in the throughput.

As a standard of the resolution, generally at the printing resolution of400 dpi or more, the character quality in which jaggies are notconspicuous is obtained. Hence, in the case of the printing resolutionof 450 dpi or more, it is desirable not to carry out the jaggiescorrection method of the invention. On the other hand, in the case ofthe printing resolution of 360 dpi or less, it is desirable to carry outthe jaggies correction method of the invention. In other words, theprocessing time can be shortened by detecting the changing point only inthe case of the printing resolution of 360 dpi or less.

Next, another embodiment will be described below. Since the formationtime of the dot differs when the dot size is varied by using the ink-jetprinting device as described above with FIG. 9, the difference arises inthe timing at which the dot is discharged from the head. That is, thetime from the input of the driving pulse to the discharge of the smalldrop is smallest since the drive time of the small drop is shortest. Thetime for discharging the large drop is largest since the drive time ofthe large drop is slowest.

For this reason, when changing the dot size and correcting jaggies, asshown in FIG. 25, with the slanting line with large inclination, theproblem that the small drop for the correction is separated arises.

Usually, the ink-jet printing device is designed so that the dischargevelocity (Vj) of the drop is preferably 5 m/s or more (more preferably 7m/s or more). Therefore, although it does not become so large gap, gapof about 10-20 micrometers will be produced. For this reason, it isremarkable with the slanting line with larger inclination than 1/1 thatthe small drop is isolated and it is visible, and since the large dropwhich constitutes the character in 1/1 or less inclination is met andthe small drop is formed, it is not so much conspicuous.

The present invention is made in consideration of the point, is changingthe jaggies correction method by inclination, and offers the optimalcorrection method which was compatible with reduction of the influenceof gap of the dot position in the jaggies correction effect.

When the example of the correction method is described, if it is madelike, the thing which correct using the small drop in 1/1 or lessinclination (FIG. 26(a) correction method), and corrects in the middledrop instead of the small drop, for example when larger than inclination1/1 (FIG. 26(b) correction method) and which is shifted so much will nothave the dot position.

Moreover, in 1/1 or less inclination, it corrects like FIG. 8(e), usingonly the small drop as another embodiment, and when larger thaninclination 1/1, as shown in FIG. 22(e), you may be made to correct inthe small drop and the middle drop.

Moreover, as another embodiment, as shown in FIG. 8(e) at the time of1/1 or less inclination, it is also possible to correct the 2 dots(namely, number of correction dots=4) before and after the changingpoint, and to correct the 1 dot of upper and lower sides of the changingpoint, when larger than inclination 1/1.

The position it becomes possible to choose the optimal with the numberof small drops, and is not based on inclination, but desirable imagequality is obtained.

As mentioned above, since according to the preferred embodiment of thepresent invention the dot which forms the outline is detected and thejaggies correction method was chosen, when half-tone processing was notperformed in the character which performed half-tone processingMoreover, since the jaggies correction method was chosen according toinclination of the slanting line part.

Also in the character which did not say that the character grew fat orjaggies were conspicuous on the contrary, and performed half-toneprocessing by small dot which is seen with the slanting line of 1/1,1/2, and 2/1, and which is corrected, the always optimal jaggiescorrection is realizable.

In that case, since the jaggies correction method is chosen according tothe level of half-tone gradation, the unnecessary load on the hostcomputer is eliminated and the optimal jaggies correction can berealized.

The ink used according to the invention is composed of at least pureware, the pigment, the wetting agent, the polyol or glycol ether withcarbon number of eight or more, the anionic or nonionic surface activeagent, the water-soluble organic solvent, and the pigment concentrationis larger than 6 wt % and the ink viscosity is larger than 8 cp(s) at 25degrees C.

The desirable color tone when usually printing in the paper (it hassufficient coloring characteristic and color-reproductioncharacteristic), high image concentration, the clear quality of imagewhich has neither the feathering phenomenon nor the color bleedingphenomenon in the character and the image,

The image with few ink strike-through phenomena which can be equal alsoto double-sided printing, the high ink dryness characteristic suitablefor high-speed printing (fixing characteristic),

The desirable image of character quality and slanting quality can beobtained by forming the step-change part circumference of the dot whichrealized high solidity, such as the light resistance and durability,upwards, and forms the character and the outline part of the graphicsimage further by the dot of the small size, and correcting thestep-change part.

Moreover, since the quality character could be printed also in lowresolution, the image could be formed by 1 path non-interlaced, andimprovement in printing speed has been realized.

Moreover, since the step-change part of binary images is detected and itwas made to create the dot data of the small size as a method of addingthe small size according to the result, the certain and optimal smalldrop addition is attained and character quality can be improved.

Moreover, gap of the dot position by the time difference produced at thetime of the formation of the small drop and the large drop appearsnotably at the time of larger inclination than 1/1, without becomingrather inferior character quality by performing the jaggies correction,the slanting line of all inclination can perform the optimal correctionand improvement in character quality can be aimed at by this.

Thus, according to the preferred embodiment of the present inventionmentioned above, by the ink-jet printing device, while realizinghigh-speed record, image quality can be improved and the ink-jetprinting device which reduced the step-change part of the shape ofstairs of the outline in the character which performed especiallyhalf-tone processing can be offered.

Furthermore, the printing on the plain paper is performed by using theink which is composed of the pure water, the pigment, the water-solubleorganic solvent, and the polyol or glycol ether with carbon number ofeight or more, and it is possible for the present invention to providethe following advantageous features:

-   the desirable color tone (which has sufficient coloring    characteristic and color-reproduction characteristic);-   high image concentration;-   clear quality of image which has neither the feathering phenomenon    nor the color bleeding phenomenon in the character and the image;-   the image which withstands double-sided printing with decreased ink    strike-through phenomena;-   high ink dryness characteristic suitable for high-speed printing    (fixing characteristic);-   high-quality image with high solidity characteristics, such as light    resistance and durability.

Moreover, it is possible to provide an ink-jet printing device and itsimage-processing method which provides high character quality in lowresolution printing (400 dpi or less).

The present invention is not limited to the above-described embodimentsand variations and modifications may be made without departing from thescope of the invention. For example, the image forming apparatuses towhich the present invention is applied may be various kinds of imageforming devices, such as printer, copier, and facsimile.

Further, the present application is based on Japanese patent applicationNo. 2003-434867, filed on Dec. 26, 2003, the entire contents of whichare hereby incorporated by reference.

1. An image-processing method comprising the steps of: detecting dotsforming a step-change part of an outline of an image of charactersand/or graphics which image is subjected to half-tone processing; andtransforming dots surrounding the dots forming the step-change partdetected by the detecting step, into respective dot data each having asize that is smaller than a size of the detected dots forming thestep-change part, wherein one of different transformation methods isselected according to an inclination of the outline in order to producethe dot data in the transforming step.
 2. The image-processing methodaccording to claim 1 wherein in the transforming step the dot datahaving the smaller size is added to a blank part of the dots forming thestep-change part.
 3. The image-processing method according to claim 1wherein in the transforming step the dot data having the smaller size isadded to a font data part of the dots forming the step-change part. 4.The image-processing method according to claim 1 wherein the differenttransformation methods in the transforming step are different in thesize of the dot data produced in the transforming step.
 5. Theimage-processing method according to claim 1 wherein the differenttransformation methods in the transforming step are different in thenumber of dots formed with the respective dot data produced in thetransforming step.
 6. The image-processing method according to claim 1wherein the different transformation methods in the transforming stepare different in a level of gradation of the image of characters and/orgraphics.
 7. An image-processing apparatus comprising: a detection unitdetecting dots forming a step-change part of an outline of an image ofcharacters and/or graphics which image is subjected to half-toneprocessing; and a transformation unit transforming, according to adetection result from the detection unit, transforming dots surroundingthe dots forming the step-change part detected by the detection unit,into respective dot data each having a size that is smaller than a sizeof the detected dots forming the step-change part, wherein thetransformation unit is provided to select one of differenttransformation methods according to an inclination of the outline inorder to produce the dot data by the transformation unit.
 8. The imageprocessing apparatus according to claim 7 wherein the detection unit isprovided to detect the dots forming the step-change part of the outlinebefore the image of characters and/or graphics is subjected to thehalf-tone processing.
 9. An image-forming apparatus including animage-formation unit forming an image on a recording paper through anink-jet printing method, and a recording-paper conveyance unit conveyingthe recording paper, the image formation unit comprising: a detectionunit detecting dots forming a step-change part of an outline of an imageof characters and/or graphics which image is subjected to half-toneprocessing; and a transformation unit transforming, according to adetection result from the detection unit, transforming dots surroundingthe dots forming the step-change part detected by the detection unit,into respective dot data each having a size that is smaller than a sizeof the detected dots forming the step-change part, wherein thetransformation unit is provided to select one of differenttransformation methods according to an inclination of the outline inorder to produce the dot data by the transformation unit.
 10. The imageforming apparatus according to claim 9 wherein the image formation unitforms the image on the recording paper using an ink which is composed ofat least pure water, a pigment, a water-soluble organic solvent, and apolyol or glycol ether with carbon number of eight or more.
 11. Theimage forming apparatus according to claim 9 wherein the image formationunit forms the image on the recording paper using an ink which iscomposed of at least pure water, a pigment, a wetting agent, an anionicor nonionic surface active agent, a water-soluble organic solvent, and apolyol or glycol ether with carbon number of eight or more, wherein theink has a pigment concentration of 6% wt or more and an ink viscosity of8 cp or more at 25 degrees C.